1. Field of the Invention
The present invention relates to a process for producing a styrenic polymer and more particularly, to a process for producing styrenic polymers without reducing their effectiveness as a molding material suitable for molded products which have excellent quality.
2. Description of the Related Arts
Various types of high-molecular weight polystyrenes have been produced for increasing the strength of polystyrene. However, attempts to elevate molecular weight of polystyrene have been disturbed by the need for retarding the reaction rate, with the result that the productivity is extremely reduced.
There have been proposed methods of solving this technical difficulty by using organic peroxides or multifunctional compounds or special reactors, wherein these methods have the defects that the reaction rate is not adequately raised and that the polystyrene produced therefrom has not had acceptable quality. A method for producing high-molecular weight polystyrene of good quality without a decrease of the productivity have not been made available yet.
For example, in Japanese Patent Publication 19511/1966 a technique of producing polystyrene by using a particular organic peroxide has been disclosed but has a shortcoming that too much organic peroxide is needed and that polystyrene has a low molecular weight, showing a low impact resistance. Japanese Patent Application Laid Open 170806/1990 discloses a method of producing a styrenic polymer with elevated impact resistance and an improved molecular weight distribution by carrying out the polymerization in the presence of a multifunctional vinyl compound, wherein this method has a defect that molded products made therefrom do not have a satisfactory degree of haze.
Further, although a method for producing styrenic resin with high molecular weight by using special reactors according to the continuous bulk polymerization method has been described in Japanese Patent Application Laid Open 70507/1989, the method has a problem of an insufficient increase of the reaction rate.
Thus, those skilled in the art have been seeking a method for producing styrenic polymers with a high molecular weight which are useful as a raw material of molded products excellent in the degree of haze and impact resistance.
The present inventors have made intensive studies in order to develop a process for producing the styrenic polymer from the above-mentioned viewpoint.
As the result, it has been found that above-mentioned objects can be achieved by polymerizing a compound consisting essentially of a styrenic monomer (aromatic vinyl monomer) in the presence of 10 to 500 ppm by weight of a particular organic peroxide. The present invention has been completed on the basis of this finding.